1. Field of the Invention
The present invention is directed in general to high-voltage integrated circuits and methods for manufacturing same. In one aspect, the present invention relates to the manufacture and use of lateral double diffusion MOS transistor (LDMOSFET) devices employing reduced surface field (RESURF) structures.
2. Description of the Related Art
High-voltage integrated circuits applications, such as high-voltage smart power applications, are constructed with integrated circuit MOS field effect transistor devices which must be able to sustain high voltages (e.g., fifty volts or greater) across the transistor device's source, body, gate, and drain terminals. With such high-voltage applications, lateral double diffusion MOS (LDMOS) transistor devices are often used to provide the high-voltage transistor devices. However, such LDMOS devices usually require thick and low doped epitaxial layer, which makes them difficult to integrate with low-voltage circuitry on the same chip. Another challenge presented with LDMOS devices is that there are typically tradeoffs between the on-resistance and breakdown voltage parameters of such devices, where the on-resistance is ideally kept low and the breakdown voltage is ideally kept high. For example, a design for an LDMOS device which increases the device breakdown voltage typically also increase the on-resistance, which is undesirable. Rapid progress in process technology has made logic devices significantly smaller for each generation. In high voltage devices, however, the required silicon distance to support needed breakdown voltage does not change. As a result, process technology advances have not significantly reduced the size of high voltage devices which must maintain a minimum breakdown voltage. Innovative device design is the only solution to reduce the die size for high voltage device. Those skilled in the art will understand that the reduced surface field (RESURF) structures can be used to redistribute the field density inside the LDMOS device, thereby maintaining the same breakdown voltage while achieving a low on-resistance with increased doping concentration of the epitaxial layer.
Accordingly, a need exists for improved semiconductor devices, especially RESURF type semiconductor devices having improved breakdown voltage, without a corresponding degradation of other important device properties. There is also a need for a high-voltage transistor device and fabrication processes to overcome the problems in the art, such as outlined above. Further limitations and disadvantages of conventional processes and technologies will become apparent to one of skill in the art after reviewing the remainder of the present application with reference to the drawings and detailed description which follow.
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the drawings have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for purposes of promoting and improving clarity and understanding. Further, where considered appropriate, reference numerals have been repeated among the drawings to represent corresponding or analogous elements.